1. Field of the Invention
This invention relates to a fluid storage and gas dispensing system which may be utilized to store high pressure liquid or other fluid, for dispensing of gas from the system and use of the dispensed gas in an application such as the manufacture of semiconductor devices and materials.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluid(s).
Such process and application areas include semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical intervention and therapy, water treatment, emergency breathing equipment, welding operations, space-based delivery of liquids and gases, etc.
U.S. Pat. No. 4,744,221 issued May 17, 1988 to Karl O. Knollmueller discloses a method of storing and subsequently delivering arsine, by contacting arsine at a temperature of from about -30.degree. C. to about +30.degree. C. with a zeolite of pore size in the range of from about 5 to about 15 Angstroms to adsorb arsine on the zeolite. The arsine is subsequently dispensed by heating the zeolite to an elevated temperature of up to about 175.degree. C. for sufficient time to release the arsine from the zeolite material.
The method disclosed in the Knollmueller patent is disadvantageous in that it requires the provision of heating means for the zeolite material, to heat the zeolite to sufficient temperature to desorb the previously sorbed arsine from the zeolite in the desired quantity.
The use of a heating jacket or other means exterior to the vessel holding the arsine-bearing zeolite is problematic in that the vessel typically has a significant heat capacity, and therefore introduces a significant lag time to the dispensing operation. Further, heating of arsine causes it to decompose, resulting in the formation of hydrogen gas, which introduces an explosive hazard into the process system. Additionally, such thermally-mediated decomposition of arsine effects substantial increase in gas pressure in the process system, which may be extremely disadvantageous from the standpoint of system life and operating efficiency, as well as safety concerns.
The provision of interiorly disposed heating coil or other heating elements in the zeolite bed itself is problematic since it is difficult with such means to uniformly heat the zeolite bed to achieve the desired uniformity of arsine gas release.
The use of heated carrier gas streams passed through the bed of zeolite in its containment vessel may overcome the foregoing deficiencies, but the temperatures necessary to achieve the heated carrier gas desorption of arsine may be undesirably high or otherwise unsuitable for the end use of the arsine gas, so that cooling or other treatment is subsequently required to condition the dispensed gas for ultimate use.
U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, describes a gas storage and dispensing system, for the storage and dispensing of gases, which overcomes the above-discussed disadvantages of the gas supply process disclosed in the Knollmueller patent. The gas storage and dispensing system of the Tom et al. patent comprises an adsorption-desorption apparatus, for storage and dispensing of a gas, e.g., a hydride gas, halide gas, organometallic Group V compound, etc. The gas storage and dispensing vessel of the Tom et al. patent reduces the pressure of stored sorbate gases by reversibly adsorbing them onto a carrier sorbent medium such as a zeolite or activated carbon material.
More specifically, such storage and dispensing system comprises: a storage and dispensing vessel constructed and arranged for holding a solid-phase physical sorbent medium, and for selectively flowing gas into and out of said vessel; a solid-phase physical sorbent medium disposed in said storage and dispensing vessel at an interior gas pressure; a sorbate gas physically adsorbed on the solid-phase physical sorbent medium; a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel, and constructed and arranged to provide, exteriorly of the storage and dispensing vessel, a pressure below said interior pressure, to effect desorption of sorbate gas from the solid-phase physical sorbent medium, and gas flow of desorbed gas through the dispensing assembly; wherein the solid-phase physical sorbent medium is devoid of trace components such as water, metals, and oxidic transition metal species (e.g., oxides, sulfites and/or nitrates) which would otherwise decompose the sorbate gas in the storage and dispensing vessel.
By the elimination of such trace components from the solid-phase physical sorbent medium, the decomposition of the sorbate gas after 1 year at 25.degree. C. and interior pressure conditions is maintained at extremely low levels, e.g., so that not more than 1-5% by weight of the sorbate gas is decomposed.
The storage and dispensing vessel of the Tom et al. patent thus embodies a substantial advance in the art, relative to the prior art use of high-pressure gas cylinders. Conventional high pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture or other unwanted bulk release of gas from the cylinder if internal decomposition of the gas leads to rapid increasing interior gas pressure in the cylinder.
Prior copending U.S. patent application Ser. No. 09/067,393 filed Apr. 28, 1998 in the names of Luping Wang and Glenn M. Tom describes a fluid storage and gas dispensing system including a storage and dispensing vessel for holding a fluid, e.g., a liquid at appropriate pressure whose vapor constitutes the fluid to be dispensed. The vessel includes an outlet port and is equipped with a dispensing assembly coupled to the outlet port, for example a valve head assembly including a dispensing valve and an outlet for selective discharge of gas deriving from liquid in the vessel.
In the Wang et al. system, a fluid pressure regulator is associated with the outlet port and may constitute part of a pressure regulator/phase separator assembly associated with the outlet port, e.g., at the neck of the vessel, to retain fluid in the vessel and, when the fluid is in liquid form, to prevent liquid from leaking to the dispensing valve and outlet. The pressure regulator and the optionally included phase separator are arranged to lie in the flow path of fluid dispensed from the vessel through the outlet port. The pressure regulator and the optionally included phase separator may be disposed interiorly or exteriorly of the vessel. Preferably, such elements are interiorly disposed, to minimize the possibility of impact and environmental exposure in use, and to minimize the leak path of the contained fluid from the vessel. When the pressure regulator and optionally included phase separator are interiorly disposed, the vessel may utilize a single weld or seam at the outlet port, to seal the vessel.
The phase separator in the Wang et al. system may comprise a porous membrane which is permeable to vapor or gas deriving from the liquid, but is not permeable to the liquid, and the phase separator preferably is disposed in a protective mode upstream of the pressure regulator so that when the contained fluid in the vessel is a liquid, the liquid is prevented from entering and interfering with the function of the pressure regulator in maintaining the liquid in the vessel, and preventing egress of liquid from the vessel.
The regulator is a flow control device, which can be set at a predetermined pressure level, to dispense gas or vapor from the cylinder at such pressure level. The pressure level set point may be superatmospheric, subatmospheric or atmospheric pressure, depending on the dispensing conditions, and the mode of gas discharge from the vessel.
The fluid storage and dispensing vessel of the parent Wang et al. patent application may be formed in the manner of a conventional high pressure gas cylinder, with an elongate main body portion having a neck of reduced cross-sectional area relative to the main body cross-section of the vessel. The vessel may in such conformation be amenable to conventional manufacture wherein the vessel is cleaned and then installed with a valve head assembly including a valve (manual or automatic) and associated pressure and flow control elements, in a manifold arrangement.
Although liquid is preferred as the contained fluid medium in the use of the fluid storage and gas dispensing system of Wang et al., it is also possible that high-pressure gas may be utilized as the fluid medium to be stored and selectively dispensed.
The storage and dispensing vessel of Wang et al. may be readily filled by setting the fluid pressure regulator at a suitably low pressure level so that the gas or vapor is at a pressure below the pressure regulator set point, using a conventional pressure regulator including a poppet element which may be biased with a biasing element such as a spring biasing element to a closed position, and which responds to pressure above the set point pressure by remaining closed, but which responds to pressure below the set point pressure by opening and allowing fluid flow therethrough.
Accordingly, the fill operation may be carried out to load the vessel with fluid to be stored and subsequently dispensed, by establishing an interior pressure level in the vessel at which the poppet element of the pressure regulator disengages from its seat, thereby allowing gas to flow into the vessel, in reverse flow fashion to the dispensing mode of the system. In this manner, the vessel may be fabricated with only one port, which thus functions to permit egress of gas from the vessel for dispensing, as well as permitting filling of the vessel with the fluid in the first instance, through the single port.
Alternatively, the vessel can be configured with dual fluid flow ports, which can accommodate separate fill and dispensing lines. For example, the dispensing port may be located at the neck of the vessel and be associated with a conventional valve head assembly, while the fill port may be provided at another location on the vessel structure.
The vessel of the Wang et al. system may be utilized for storage and dispensing of any suitable fluids, such as for example hydride fluids (e.g., arsine, phosphine, stibine, silane, etc.) and acid gases (e.g., hydrogen fluoride, hydrogen chloride, chlorine, boron trichloride, boron trifluoride, halogenated silanes and disilanes, etc.) for use in semiconductor manufacturing operations.
In use, a dispensing valve may be provided as part of the dispensing assembly associated with the port of the vessel, and such valve may be opened, manually or automatically, to permit gas to flow through the porous membrane or phase separator element, when present, and through the regulator for discharge of the gas from the fluid storage and dispensing system, and subsequent flow to a downstream process system, such as an ion implantation apparatus, chemical vapor deposition chamber, semiconductor equipment cleaning station, etc.
The Wang et al. system may thus be employed to practice a method for storage and dispensing of a fluid, comprising the steps of:
containing the fluid in a confined state against a fluid pressure regulator in a fluid flow path closed to fluid flow downstream of the fluid pressure regulator; and
selectively dispensing the confined fluid by opening the fluid flow path to fluid flow downstream of the fluid pressure regulator, and discharging fluid at a rate determined by the fluid pressure regulator,
optionally wherein the contained fluid is a liquid and the fluid during dispensing is phase-separated upstream of the fluid pressure regulator, to permit only gas to be discharged from the fluid contained in a confined state.
While the approach of the Wang et al. system is generally viable, it is possible that under long-term storage conditions of the fluid vessel, condensation of liquid on the downstream side of the membrane can occur. For example, if the vessel is reposed on its side and the liquid volume extends above the height of the permeable phase-separator membrane in such position, then a small potential gradient is present and is equal to the gravitational potential associated with such liquid "head." In order to equilibrate this liquid head potential, liquid will condense on the valve side of the membrane until the respective liquid levels on the opposing sides of the membrane have equalized. There is a need to remedy this shortcoming.
Additionally, for gas storage and dispensing vessels of the high pressure cylinder type, such as are conventionally employed for boron trifluoride (BF.sub.3), the gas storage capacity of the system is usually determined and limited by the cylinder pressures. The pressures that would be necessary for liquefaction of the gas in such instances may be prohibitive, so that the Wang et al. system is not readily susceptible for such use. There is a need to remedy this shortcoming.
Further to the above, the gas cylinder vessels conventionally used for compressed gas service typically utilize valve inlets, as measured by National Gas Taper (NGT) standards, of 3/4 inch NGT, 1/2 inch NGT, and smaller. In order to usefully exploit the Wang et al. system of the parent application, embodying a "regulator in a bottle" approach, larger cylinder inlets are required than are currently conventionally available. The Compressed Gas Association's (CGA's) largest recommended compressed gas cylinder inlet is a 1.5 inch NGT-11 1/2 tpi (threads per inch) opening having a minimum diameter of 1.79 inch. Openings larger than 3/4 inch NGT are typically designed for applications in which high flows and larger cylinders (&gt;50 liters internal volume) are required. The inventors are not aware of any cylinders with volumes of less than 50 liters that have openings larger than 1 inch NGT, and it is very unlikely that any openings larger than 1 inch NGT have been employed for cylinders with volumes of less than 20 liters.
In order to commercially enable the Wang et al. "regulator in a bottle" approach of the parent patent application, it is necessary to provide a cylinder that satisfies United States Department of Transportation (USDOT) packaging standards, has a larger inlet opening than is conventionally available, and can withstand pressures in the range of from about 1000 to about 5000 pounds per square inch (psi). No such vessel has been proposed or fabricated by the prior art, and none is commercially available. There is a need to remedy this shortcoming.
There is therefore a need in the art to provide improved fluid storage and delivery systems for selective dispensing of gases that overcome the various deficiencies described above.
Relative to the state of the art and the invention as described more fully hereinafter, pertinent art includes the following references: U.S. Pat. No. 3,590,860 to Stenner (a manually adjustable regulator valve for a liquid propane cartridge, including a regulator diaphragm and actuating spring assembly); U.S. Pat. No. 4,836,242 to Coffre et al. (a pressure reducer for supplying electronic grade gas, including a bellows and inlet valve, with a solid particles filter disposed between the bellows and a low pressure outlet); U.S. Pat. No. 5,230,359 to Ollivier (a diaphragm-based pressure regulator for a high pressure gas cylinder, wherein a valve is positioned in the regulator for adjustably throttling the flow of pressurized fluid); U.S. Pat. No. 3,699,998 to Baranowski, Jr. (a calibratable pressure regulator in which leaf spring fasteners are utilized to retain the regulator components in position); U.S. Pat. No. 3,791,412 to Mays (a pressure reducing valve for high pressure gas containers, including a pair of valve elements for dispensing low pressure throttled fluid); U.S. Pat. No. 3,972,346 to Wormser (pressure regulator featuring a U-ring seal poppet assembly); U.S. Pat. No. 4,793,379 to Eidsmore (button-operated valve for main shut-off and flow control of a pressurized gas cylinder, using magnetic actuation of valve components); U.S. Pat. No. 2,615,287 to Senesky (a gas pressure regulator including diaphragm and diaphragm-clamping member elements); U.S. Pat. No. 4,173,986 to Martin (pressurized gas flow control valve including pressure regulator and responsive poppet valve structure); U.S. Pat. No. 3,388,962 to Baumann et al. (pressurized gas fuel metering device including sintered metal pellet flow element); U.S. Pat. No. 1,679,826 to Jenkins (fluid pressure regulator for high pressure container, utilizing diaphragm element and gas filtering means comprising a felt strip); U.S. Pat. No. 2,354,283 to St. Clair (fluid pressure regulator for liquefied petroleum gas tanks, comprising pressure actuated diaphragm with flow restrictor structure to minimize vibration); U.S. Pat. No. 5,566,713 to Lhomer et al. (gas flow control dispensing assembly including piston-type pressure regulator and block reducer/regulator means); U.S. Pat. No. 5,645,192 to Amidzich (valve assembly for relieving excess gas pressure in a container, comprising sealing ring/spring assembly); U.S. Pat. No. 5,678,602 to Cannet et al. (gas control and dispensing assembly for a pressurized gas tank, including reducer and regulator means with indexed flowmeter valve); U.S. Pat. No. 2,793,504 to Webster (valve for pressurized fluid container including pressure reducer and regulator and spring bias closure means); U.S. Pat. No. 1,659,263 to Harris (regulator for pressurized gas cylinder including a diaphragm and anti-friction washer between diaphragm and annular seat of regulator); U.S. Pat. No. 2,047,339 to Thomas (liquefied petroleum gas storage apparatus including flow control unit and leakage prevention valve); and U.S. Pat. No. 3,994,674 to Baumann et al. (detachable burner assembly for container of pressurized liquefied combustible gas, including a regulator valve assembly).
It is accordingly an object of the present invention to provide an improved fluid storage and dispensing system for the selective dispensing of gases, which overcomes the aforementioned deficiencies of prior practice.
It is another object of the invention to provide an improved fluid storage and dispensing system for the selective dispensing of gases, characterized by significant advantages in cost, ease of use, and performance.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.